Nano versus bulk: Evaluating the toxicity of lanthanum, yttrium, and cerium oxides on Enchytraeus crypticus

Considering the increase in demand for rare earth elements (REEs) and their accumulation in soil ecosystems, it is crucial to understand their toxicity. However, the impact of lanthanum, yttrium and cerium oxides (La₂O₃, Y₂O₃ and CeO₂, respectively) on soil organisms remains insufficiently studied. This study aims to unravel the effects of La₂O₃, Y₂O₃ and CeO₂ nanoparticles (NPs) and their corresponding bulk forms (0, 156, 313, 625, 1250 and 2500 mg/kg) on the terrestrial species Enchytraeus crypticus. The effects on survival, reproduction (21 days (d)), avoidance behavior (2 d) and DNA integrity (2 and 7 d) of E. crypticus were evaluated. No significant effects on survival were observed. For La₂O₃, the bulk form affected more endpoints than the NPs, inducing avoidance behavior (1250 mg/kg) and DNA damage (1250 mg/kg - 2 d; 2500 mg/kg - 7 d). The Y₂O₃ NPs demonstrated higher toxicity than the bulk form: decreased reproduction (≥ 1250 mg/kg); induced avoidance behavior (≥ 625 mg/kg) and DNA damage (≥ 156 mg/kg - 2 d; 2500 mg/kg - 7 d). For CeO₂, both forms exhibited similar toxicity, decreasing reproduction (625 mg/kg for bulk and 2500 mg/kg for NPs) and inducing DNA damage at all tested concentrations for both forms. REEs oxides toxicity was influenced by the REEs type and concentration, exposure time and material form, suggesting different modes of action. This study highlights the distinct responses of E. crypticus after exposure to REEs oxides and shows that REEs exposure may differently affect soil organisms, emphasizing the importance of risk assessment.